Michelson interferometers are used in many commercial applications. Performance characteristics and stability limitations of various designs are well known and understood. Slight misalignments of optical elements in a conventional interferometer cause modulation changes that may significantly affect the performance of the interferometer. There have been numerous attempts in the design of commercial interferometers, Michelson interferometers included, to reduce misalignments and/or the effects of misalignments. Some of these attempts include passive means, such as using cube corner mirrors, retro-mirrors, and/or other means to compensate for undesirable effects. Other attempts have used active means such as dynamic mirror alignment or active thermal control, among others. Alternatively, adjustment mechanisms are available to enable periodic or necessary reestablishment of the relationships of the optical elements to maintain acceptable alignment conditions.
Generally, Michelson interferometers produce an alternating optical signal by splitting an input beam of light into two portions, inducing an alternating path difference in one of the portions, and recombining the portions at the exact point of initial splitting. Maintaining flatness and consistent geometric relationship (to a wave front) of the mirror element that produces the path difference during a scan (e.g., movable mirror) is important to system performance, stability and ultimately instrument data quality. Any short or long term change (commonly referred to as optical instability) in the geometric relationship or flatness of either the fixed or movable mirrors to the wave front may produce compromised results. Similar results occur when the beam splitter changes flatness or angle relative to the wave front.
Spectral resolution of an interferometer is related to the distance the movable mirror moves during the scan. In the field of Fourier transform infrared (FTIR) spectroscopy instrument design, in particular, movement of the movable mirror is typically achieved via a mechanical bearing. There are many bearing implementations having a wide spectrum of costs and complexity.
Flat springs (bearings or bearing flexures) have been used with interferometers. U.S. Pat. No. 7,630,081, to Ressler et al. (Dec. 8, 2009), which is hereby incorporated by reference, is an example of conventional interferometers. U.S. Pat. No. 7,630,081 addresses use of a pair of bearing flexures, including disclosure of material selection and geometry, to achieve a high degree of performance and thermal/mechanical stability at a relatively low cost and relatively small size. However, such conventional interferometers may have limited resolution capability due to inherent bearing travel restrictions. Thus, there is a need for high performance, reliable interferometers that are capable of longer bearing travel providing greater resolution, e.g., for mid-level laboratory markets.